1. Field of the Invention
The present invention relates to a method for manufacturing a honeycomb structure.
2. Discussion of the Background
In recent years, particulates such as soot contained in exhaust gases discharged from internal combustion engines of vehicles such as buses and trucks, and construction machines have raised serious problems as contaminants harmful to the environment and the human body. For this reason, various honeycomb filters, which use a honeycomb structure made of porous ceramics, have been proposed as filters that collect particulates in exhaust gases and purify the exhaust gases.
JP2004-154718 A describes a honeycomb filter that is used for purifying exhaust gases and is formed by a honeycomb structure, and a method for manufacturing the honeycomb structure. This honeycomb structure is manufactured by combining a plurality of kinds of honeycomb fired bodies having different shapes by interposing an adhesive layer.
FIG. 1 is a perspective view that schematically shows one example of a conventional round pillar-shaped honeycomb structure. In the honeycomb structure 250, as shown in FIG. 1, three kinds of honeycomb fired bodies 220, 230, and 240 are combined with one another by interposing an adhesive layer 254 to form a ceramic block 255, and a sealing material layer 253 is further formed on a peripheral face 256 of the ceramic block 255.
The honeycomb fired body 220 is a honeycomb fired body whose cross section perpendicular to a longitudinal direction (the direction shown by an arrow C in FIG. 1) has a shape surrounded by two straight lines and one curved line (hereinafter, referred to also as an A-type honeycomb fired body). The honeycomb fired body 230 is a honeycomb fired body whose cross section perpendicular to the longitudinal direction has a shape surrounded by three straight lines and one curved line (hereinafter, referred to also as a B-type honeycomb fired body). The honeycomb fired body 240 is a honeycomb fired body whose cross section perpendicular to the longitudinal direction has a shape surrounded by four straight lines (hereinafter, referred to also as a C-type honeycomb fired body).
FIG. 2A is a perspective view that schematically shows a C-type honeycomb fired body, and FIG. 2B is a cross-sectional view taken along line A-A of FIG. 2A.
Moreover, each of the honeycomb fired bodies 240 has a structure in which a large number of cells 241 are disposed in parallel with one another in the longitudinal direction (the direction shown by an arrow B in FIG. 2A), and a cell wall 242 between the cells 241 is allowed to function as a filter. That is, as shown in FIG. 2B, the ends of either the exhaust gas inlet side or the exhaust gas outlet side of each of the cells 241 formed in the honeycomb fired body 240 is plugged with a plug 246 so that the exhaust gas entering one cell 241 is discharged from another cell 241 after having always passed through a cell wall 242 between the cells 241; thus, when exhaust gas passes through the cell wall 242, particulates are captured by the cell wall 242, so that the exhaust gas is purified.
Here, each of the honeycomb fired bodies 220, 230 and 240 has a structure in which a large number of cells are disposed in the longitudinal direction, with either one of the ends of each of the cells being plugged with a plug, so that each honeycomb fired body is allowed to function as a filter.
Conventionally, each of these honeycomb fired bodies is manufactured through the following processes. First, ceramic powder, a binder, a dispersant solution, and the like are mixed to prepare a mixed composition for manufacturing a molded body, and this mixed composition is loaded into an extrusion-molding machine comprising an extrusion-molding die so that an extrusion-molding process is carried out to manufacture an extrusion-molded body. Next a cutting process for cutting the extrusion-molded body into a predetermined length is carried out.
By using these processes, a honeycomb molded body, having approximately the same shape as the shape of each of the honeycomb fired bodies to be manufactured and having a large number of cells disposed in parallel with one another in a longitudinal direction with a cell wall therebetween, is manufactured.
Subsequently, the resulting honeycomb molded body undergoes a drying process to be dried, and then undergoes a plugging process in which a plug material paste is injected into predetermined cells of the honeycomb molded body that has been dried so that the cells are plugged. The honeycomb molded body to which the plug material paste has been injected is heated to carry out a degreasing process for thermally decomposing organic matters such as the binder in the honeycomb molded body, and a firing process is further carried out on the degreased honeycomb molded body so that a honeycomb fired body is manufactured. The contents of JP2004-154718 A are incorporated herein by reference in their entirety.